The present invention pertains to the treatment of food processing wastewaters to provide a potentially important feed value or fertilizer by-product and a directly dischargeable or recyclable effluent. In particular, the process and related method are especially adapted to the treatment of dairy plant process wastewater streams to provide a valuable animal feed supplement or a fertilizer and a dischargeable effluent or a reusable water source which is clean and environmentally safe.
Food processing operations, such as dairy plants, suffer significant product losses from spills, rinsing, and clean-in-place procedures in which the water borne product, constituting a random liquid mixture, is sewered or wasted. This wastewater may be treated on site in a captive wastewater treatment system or, more typically, discharged into a municipal sewerage system for treatment in a central municipal wastewater treatment facility. The first means of treatment on site requires a substantial capital expenditure and the alternate municipal treatment often subjects the plant operator to substantial surcharges because of the typically high suspended solids, biochemical oxygen demand (BOD), and phosphorous or other mineral loadings of the discharged effluent.
In the dairy industry, and in cheese plants in particular, whey produced as a by-product of the cheese making process was previously discharged as a wastewater. Today, this cheese making by-product is processed to recover protein, lactose and minerals. However, the effluent from spills, rinses and cleaning procedures is still handled as a wastewater.
U.S. Pat. No. 5,173,190 describes the reconditioning and reuse of poultry processing rinse water, including the basic steps of screening, flotation, and membrane separation. The system is directed to reconditioning the rinse water for recirculation and reuse, but does not provide for any use of the suspended solids removed in the flotation step or the concentrate removed by membrane filtration.
U.S. Pat. No. 3,917,526 describes a multi-stage separation system which includes, as two of the steps, foam flotation and membrane separation. One specific application of the process is identified as the separation of cheese whey to recover protein and lactose. In particular, the concentrate pressure at the membrane separation stage is utilized to operate a jet pumping adductor to assist in withdrawing the foam and entrained solids from the foam flotation apparatus.
However, whey recovery processes in the dairy industry are well established. Whey is a known and relatively stable product of a cheese making process and is capable of being processed for protein, lactose and mineral recovery in a well known and straightforward manner. Dairy and other food processing plant wastewaters, on the other hand, contain a wide variety of other contaminants and foreign matter resulting from rinsing and cleaning processes, such as grit, debris, detergents and the like. These wastewaters also typically have high phosphorous loadings. As a result, these dairy and food processing plant wastewaters have a widely varying and often unpredictable makeup resulting in the simple expedient of discharge to the sewer for conventional wastewater treatment and no recoverable by-product.
Nevertheless, a typical dairy plant may lose approximately 2.5% of its fluid milk intake to waste related to spillage, rinsing and cleaning. Therefore, it would be most desirable to be able to capture the suspended and dissolved solids lost in these wastewaters to simultaneously recover a potentially valuable feed value by-product and provide an effluent clean enough for direct discharge or reuse.